Lightweight Electric/Hybrid Vehicle Design

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Current EV design approaches 19 It is assumed that sealed batteries are to be used and consequently a battery voltage of 96 V was chosen to optimize the efficiency of motor and controller and particularly with an eye to controller cost. 200 V MOSFETS are near optimal at 100 V DC. A battery of 15 Ah 96 V weighs 40 kg (for comparison 24 V 60 Ah weighs 35 kg). In lead–acid 36 Wh/kg is achieved, while for comparison nickel hydride cells could offer 80 cells x 1.2 V x 25 Ah in a weight of 30 kg. The motor has to deliver a torque of about 40 Nm maximum and consequently a pancaketype design was chosen. Induction motors were rejected due to low efficiency and large mass for this duty. The four practical contenders are: permanent magnet brushless DC; permanent magnet DC brush pancake motor; DC series motor or switched reluctance motor. A tabulated comparison at Fig. 1.17(a) compares results. As can be seen, the permanent magnet brushless DC motor is the optimum performer at the two key cruise conditions. It has been estimated that with regenerative braking and flat terrain, a range of 70 km could be achieved with a 96 V 15 Ah lead–acid battery. The 25 Ah nickel hydride pack could give 120 km. However, 70 km is quite adequate for average daily use. 1.3.6 SMALL CAR The small electric car is in the Mini or Fiat 500 class. Such a vehicle would weigh 750 kg and accelerate from 0 to 50 mph (80 km/h) in 12 seconds and have a range of 80 km with lead–acid batteries. The motor power would be 20 kW peak. As originally there were only aqueous batteries available, battery voltage was limited to 120 V DC by the tracking that took place across the terminals of the batteries due to electrolyte leakage. Two battery technologies were available: lead–acid and nickel–cadmium and vehicles were designed with efficiency = 25%, that is 188 kg of batteries if efficiency is expressed as battery mass/gross vehicle mass (for lead–acid 60 Ah 120 V 7.2 kWh and for nickel–cadmium 85 Ah 120 V 9.9 kWh). Single quadrant MOSFET choppers were developed by Curtis and others to supply DC brushed series motors. The main advantage of this system was low cost (for example, lead–acid battery £900 in 1996; quadrant chopper £500; motor DC series £750). However, the apparent cheapness of this system is deceptive because: (a) fitting regeneration can raise the battery voltage to 150 V – an unsustainable level for some choppers – consequently friction braking was often used; (b) a separate battery charger was required. More recently sealed battery systems have become available and batteries of around 200 V are possible in two technologies, lead–acid foil and nickel hydride. These batteries are used with 600 V IGBT transistors which can operate at voltages up to 350 V DC. Battery capacity becomes limited if other services such as cabin temperature control/lighting/ battery thermal management are taken into consideration. A small engine driven generator transforms this problem and it is perhaps worth noting Honda have achieved full CARB approval for their small lean burn carburettor engines with the discovery that needle jet alignment is critical to emissions control and negates the need for catalytic converters. All motor technologies are viable at 196 V; however, the practical consideration is that inverters are more costly than choppers which accounts for the popularity of DC brushed motors/choppers. To counteract the inverter cost premium, the electronically commutated machines have been designed for 12 000 rpm, to reduce the motor torque (DC brush machine 20 kW at 5000 rpm; other types 20 kW at 12 000 rpm). Another benefit of the higher transistor voltage capability is that the inverters/choppers can function as battery chargers direct off 220/240 V without additional equipment. High rate charging is possible where the supply permits. All electronically commutated machines provide regeneration. The motor comparison is tabulated at Fig. 1.17(b). All the machines deliver constant power (20 kW) over a 4:1 speed range, making gear changing unnecessary. The induction/brushless motors are assumed to use vector control.
20 Lightweight Electric/Hybrid Vehicle Design (a) PM BDC Brushed PM DC series Switched pancake motor reluctance Size (mm) 200 × 100 200 × 100 200 × 175 200 × 150 Weight (kg) 10 10 18 14 Rating 3 @ 750 3 @750 3 @750 3 @1500 (kW@rpm@V) 40 40 60 70 3 @1500 3 @1500 3 @1500 70 80 80 Efficiency 0.3/750 80% 3/750 75% 3/750 70% 3/750 80% (motor 0.75/750 94% 750/750 80% 750/750 70% 750/750 85% only) 3/1500 93% 3/1500 85% 3/1500 80% 3/1500 85% (b) Brushless Induction Switched Brushed DC PM motor motor reluctance DC motor Speed (rpm) 3000 3000 3000 1250 Torque (Nm) rising to: 64 64 154 Speed (rpm) 12 000 12 000 5000 Torque (Nm) 16 16 38.5 Voltage (V) 150 AC 150 75–150 192 Current (A) 126–81 AC 164–106 AC 180–90 DC 122 DC Power (kW) 20 20 20 20 Frequency (Hz) 800 400 800 (equiv. 125 Hz) Weight (kg) Efficiency 12 25 20 50 % @ 3000 95 90 92 (1250) 80 % @ 12 000 97 92 94 (5000) 85 Cooling oil oil oil air (c) PM (DC) Induction Switched DC brushless motor reluctance brush Speed (rpm) 1000 1000 1000 1000 Torque (Nm) 2866 2866 2866 2866 at speed (rpm) 4000 4000 4000 4000 Torque (Nm) 716 716 716 716 Voltage (V) 380 380 190/380 500 Current (A) 753–486 980–630 1000/500 520 Power (kW) 300 300 300 300 Frequency (Hz) 1056 133 266 (133 equiv.) Weight (kg) 300 600 500 1000 Efficiency % @ 1000 95 93 94 85 % @ 4000 97 95 96 89 Cooling oil oil oil air Fig. 1.17 Motor comparisons for three vehicle categories (the four motor types are also discussed in Chapter 4).
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PART TWO Battery/fuel-cell EV desig
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5 Battery/fuel-cell EV design packa
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(a) cell voltage 2,5 V 2,0 1,5 1,0
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Varta Electric Power: Nickel-metal-
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700 600 500 400 CurrentmA 300 (a) 2
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Battery/fuel-cell EV design package
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Intake filter Intercooler High spee
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Fig. 5.22 Bradshaw Envirovan. Batte
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6.1 Introduction 6 Hybrid vehicle d
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6.2 Hybrid-drive prospects Hybrid v
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TRAVEL ELECTRIFIED, % 80 70 60 STRA
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Hybrid vehicle design 147 750 kg to
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M [Nm] 500 450 400 350 300 250 200
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6.3.6 TAXI HYBRID DRIVE Hybrid vehi
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Hybrid vehicle design 153 The Rover
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Hybrid vehicle design 155 as a star
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Hybrid vehicle design 157 injection
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Hybrid vehicle design 159 In ‘sta
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Hybrid vehicle design 161 power and
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Hybrid vehicle design 163 The batte
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Hybrid vehicle design 165 into mech
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Hybrid vehicle design 167 drive ele
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Hybrid vehicle design 169 The view
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Hybrid vehicle design 171 6.5.4 ADV
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Lightweight construction materials
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(a) (d) (e) Lightweight constructio
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(a) Creepstrain dE/dt (b) 3.0 2.0 1
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(a) M b Mb Mt 3 2 1 T (b) (c) t s T
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Design for optimum body-structural
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Lightweight Electric/Hybrid Vehicle Design

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